Maximum Wall Shear Stress Research Articles

A Simplified Computational Workflow for Evaluation of Aortic Hemodynamics After Frozen Elephant Trunk Intervention in Type A Aortic Dissection

This study aimed to predict the hemodynamic performance of frozen elephant trunk (FET) intervention in surgically repaired type A aortic dissection (TAAD) patients through computational simulations of post-operative scenarios. Patient-specific geometries of a single patient were reconstructed from pre- and post-FET intervention computed tomography angiography (CTA) images. The pre-FET geometry was used to create post-FET geometry through anatomical modifications and a simplified finite element simulation to inflate the stented true lumen (TL) segment. Computational fluid dynamics (CFD) simulations were then performed on the virtually created post-FET geometry, and the results were compared with those obtained with the actual post-FET geometry. Various intervention scenarios with different stent-graft (SG) lengths and TL volume expansion were also simulated and compared to study their impacts on hemodynamic performance. A good overall agreement was achieved between the virtual and real post-FET models, with the maximum difference in true and false lumen (FL) pressures along the dissected aorta being 4.2%. Simulation results for the actual intervention revealed high wall shear stress (WSS) and pressure around a distal tear that was found to have expanded on post-FET scan. Extending the SG length dramatically reduced the maximum WSS and pressure around the distal tear. This pilot study demonstrates the feasibility of using the simplified simulation workflow for personalized assessment of aortic hemodynamics following FET intervention in repaired TAAD. Further studies in a large patient cohort are warranted.

Differences in Carotid Artery Geometry and Flow Caused by Body Postural Changes and Physical Exercise.

Different body postures and physical exercises may lead to changes in arterial geometry and hemodynamics, which may be associated with the distribution of atherosclerosis lesions. This study was aimed at investigating potential geometric and hemodynamic changes of the carotid bifurcation in different body postures and after high-intensity interval training (HIIT) workouts. Three-dimensional vascular ultrasound (3DVUS) and Doppler ultrasound images were acquired for 21 healthy participants (aged 29 ± 6 y, 14 men and 7 women) in different body postures (sitting and three sleeping postures [supine, left lateral and right lateral]) and after physical exercises. The common carotid artery (CCA) and internal carotid artery (ICA) diameters of the left carotid artery were found to increase significantly from supine to left lateral (both p <0.05). CCA diameters (p < 0.05) and ICA/CCA diameter ratio (p < 0.01) of the left carotid artery changed significantly from supine to sitting. Significant differences in CCA peak systolic velocity (CCA PSV, p < 0.001), CCA end-diastolic velocity (CCA EDV, p < 0.001), CCA pulsatility index (CCA PI, p < 0.001) and maximum velocity-based wall shear stress at the CCA (WSS(max) at the CCA, p < 0.001) were identified in different postures. After physical exercises, significant increases were observed in the CCA diameter (p < 0.001), CCA PSV (p < 0.001), ICA PSV (p < 0.05), WSS(max) at the CCA (p < 0.001) and WSS(max) at the ICA (p < 0.05), as were significantly lower values of the CCA EDV (p < 0.01) and ICA/CCA PSV ratio (p < 0.05). Side-to-side differences were also detected in different postural change scenarios and after physical exercise; more significant differences were found to occur only in the left-sided carotid artery. Significant differences were identified under postural change and after physical exercise among healthy adults, suggesting that daily activity has an effect on the carotid bifurcation. These changes may be associated with formation and development of carotid atherosclerosis. Moreover, these side differences might be severe for patients and worth further attention in clinical practice.

Computational study of the blood hemodynamic inside the cerebral double dome aneurysm filling with endovascular coiling

The rupture of the aneurysm wall is highly associated with the hemodynamic feature of bloodstream as well as the geometrical feature of the aneurysm. Coiling is known as the most conventional technique for the treatment of intracranial cerebral aneurysms (ICA) in which blood stream is obstructed from entering the sac of the aneurysm. In this study, comprehensive efforts are done to disclose the impacts of the coiling technique on the aneurysm progress and risk of rupture. The computational fluid dynamic method is used for the analysis of the blood hemodynamics in the specific ICA. The impacts of the pulsatile blood stream on the high-risk region are also explained. Wall shear Stress (WSS) and Oscillatory shear index (OSI) factors are also compared in different blood viscosities and coiling conditions. According to our study, the hematocrit test (Hct) effect is evident (25% reduction in maximum WSS) in the two first stages (maximum acceleration and peak systolic). Our findings present that reduction of porosity from 0.89 to 0.79 would decrease maximum WSS by about 8% in both HCT conditions.

Computational assessment of venous anastomosis angles and graft configurations in arteriovenous graft

Arterio-venous grafts are a viable option for hemodialysis as long-term vascular access. The leading cause of Arterio-venous Grafts (AVG) failure is the development of intimal hyperplasia (IH), primarily found in vessel areas with unfavorable hemodynamic conditions. Computational Fluid Dynamics (CFD) is utilized in this study to assess the effect of some geometrical designs at venous anastomosis on these conditions.At first, models with various anastomosis angles are designed. Results represent that the maximum Wall Shear Stress (WSS) in the model with the anastomosis angle of 15° has decreased from 34.07 Pa to 17.48 Pa (48.69%) compared to the conventional model. Moreover, vortices and regions with high WSS at vein anastomosis reduce remarkably.In the second part, to lessen the unfavorable hemodynamic conditions inspired by the rotational blood flow in the aorta, the graft is designed with several cross-sectional ridges to induce a swirl flow. Three essential hemodynamic parameters, including Oscillatory Shear Index (OSI), Time Averaged Wall Shear Stress (TAWSS), and Relative Residence Time (RRT) in pulsating blood flow models, are extracted, and the outcomes are compared to conventional AVG.Finally, according to the results of the previous sections, an optimized model is proposed. Comparing this model with the conventional one illustrates more than 90% decrement in regions related to high OSI values and a 22.84% reduction in RRT values as the main hemodynamic parameters to assess the areas with a high risk of IH development.

Wall Shear Stress Associated with Stroke Occurrence and Mechanisms in Middle Cerebral Artery Atherosclerosis.

Various mechanisms are involved in the etiology of stroke caused by atherosclerosis of the middle cerebral artery (MCA). Here, we compared differences in plaque nature and hemodynamic parameters according to stroke mechanism in patients with MCA atherosclerosis. Consecutive patients with asymptomatic and symptomatic MCA atherosclerosis (≥50% stenosis) were enrolled. MCA plaque characteristics (location and plaque enhancement) and wall shear stress (WSS) were measured using high-resolution vessel wall and four-dimensional flow magnetic resonance imaging, respectively, at five points (initial, upstream, minimal lumen, downstream, and terminal). These parameters were compared between patients with asymptomatic and symptomatic MCA atherosclerosis with infarctions of different mechanisms (artery-to-artery embolism vs. local branch occlusion). In total, 110 patients (46 asymptomatic, 32 artery-to-artery embolisms, and 32 local branch occlusions) were investigated. Plaques were evenly distributed in the MCA of patients with asymptomatic MCA atherosclerosis, more commonly observed in the distal MCA of patients with artery-to-artery embolism, and in the middle MCA of patients with local branch occlusion. Maximum WSS and plaque enhancement were more prominent in the minimum lumen area of patients with asymptomatic MCA atherosclerosis or those with local branch occlusion, and were more prominent in the upstream area in those with artery-to-artery embolism. The elevated variability in the maximum WSS was related to stroke caused by artery-to-artery embolism. Stroke caused by artery-to-artery embolism was related to plaque enhancement and the highest maximum WSS at the upstream point of the plaque, and was associated with elevated variability of maximum WSS.

Studies on the elbow corrosion associated with the wall-wetting process in stratified and wave flows

ABSTRACT The flow-induced corrosion in gas-liquid flow usually occurs in the petrochemical and transportation industries, which has become a hot topic, especially for the elbow system. In this paper, a series of simulations using the VOF method and SST k-ω turbulence models were carried out to investigate the temporal and spatial distributions of the water wetting process in the elbow system. Combined with experiments, the relationship between the dynamic hydrophilic process and the corrosion mechanism was revealed. The results show that there is a stratified flow in the pipe at low speed. Wetness is always present in the inner wall of the elbow, and the corrosion rate reduces as the axial angle increases. As the velocity increases, the flow pattern changes to wave flow. Part of the water in the inner wall is entrained into the gas phase and thrown out onto the outer wall to form the water wetting. The location of maximum wall shear stress is transferred to outer wall, causing an increment of corrosion rate. The corrosion rate of the outer wall increases with the axial angle.

Wall Shear Stress Measurement in Carotid Artery Phantoms with Variation in Degree of Stenosis Using Plane Wave Vector Doppler

Wall shear stress (WSS) plays an important role in the formation, growth, and rupture of atherosclerotic plaques in arteries. This study measured WSS in diseased carotid artery phantoms with degrees of stenosis varying from 0 to 60% with both steady and pulsatile flow. Experiments were performed using in silico and real flow phantoms. Blood velocities were estimated using plane wave (PW) vector Doppler. Wall shear stress was then estimated from the velocity gradient near the wall multiplied by the viscosity of a blood-mimicking fluid. The estimated WSS using the in silico phantom agreed within 10% of the ground-truth values (root-mean-square error). The phantom experiment showed that the mean WSS and maximum WSS increased with the increasing degree of stenosis. The simulation and experiment results provide the necessary validation data to give confidence in WSS measurements in patients using the PW vector Doppler technique.

DESIGNING OF DIFFERENT TYPES OF GYROID SCAFFOLD ARCHITECTURE TO ACHIEVE PATIENT-SPECIFIC OSSEOINTEGRATION FRIENDLY MECHANICAL ENVIRONMENT

Porous three-dimensional scaffolds provide a favorable environment for the regeneration of tissues and organs to recover the injured tissue in terms of structure and biological function. Proper design of scaffold architecture is a crucial factor for tissue engineering. The mechanical properties and performance of the scaffold depend on the scaffold architecture, material, and geometry. In this study, numerical analysis is performed on four types of gyroids to see the variation of effective elastic modules in three different directions. The fluid flow induces wall shear stress (WSS), considering the Newtonian fluid is also investigated. Initially, the WSS is evaluated through computational fluid dynamics simulation and compared to previous literature. A good agreement between the results of published literature and those initial works encourages dealing with several cases by varying different parameters. The effect of scaffold architecture, pore size, and flow direction on WSS is studied using 16 different gyroid models. A significant reduction of scaffold stiffness can be achieved with porosity, and WSS increases with a decrease in pore size. Inlet flow direction also has a good influence on WSS. Fluid flow perpendicular to the gyroid cross-sectional area gives maximum WSS and gradually decreases with an increase in direction angle. The present study can be used to reference a specific scaffold design in tissue engineering.

Irregular anatomical features can alter hemodynamics in Takayasu arteritis

ObjectiveTakayasu arteritis (TA) is a difficult disease to deal with because there are neither reliable clinical signs, laboratory biomarkers, nor a single noninvasive imaging technique that can be used for early diagnosis and disease activity monitoring. Knowledge of aortic hemodynamics in TA is lacking. This study aimed to fill this gap by assessing hemodynamics in patients with TA using image-based computational fluid dynamics (CFD) simulations. MethodsEleven patients with TA were included in the present study. Patient-specific geometries were reconstructed from either clinical aortic computed tomography angiography or magnetic resonance angiography studies and coupled with physiological boundary conditions for CFD simulations. Key anatomical and hemodynamic parameters were compared with a control group consisting of 18 age- and sex-matched adults without TA who had healthy aortas. ResultsCompared with controls, patients with TA had significantly higher aortic velocities (0.9 m/s [0.7, 1.1 m/s] vs 0.6 m/s [0.5, 0.7 m/s]; P = .002), maximum time-averaged wall shear stress (14.2 Pa [9.8, 20.9 Pa] vs 8.0 Pa [6.2, 10.3 Pa]; P = .004), and maximum pressure drops between the ascending and descending aorta (36.9 mm Hg [29.0, 49.3 mm Hg] vs 28.5 mm Hg [25.8, 31.5 mm Hg]; P = .004). These significant hemodynamic alterations in patients with TA might result from abnormal anatomical features including smaller arch diameter (20.0 mm [13.8, 23.3 mm] vs 25.2 mm [23.3, 26.8 mm]; P = .003), supra-aortic branch diameters (21.9 mm [18.5, 24.6 mm] vs 25.7 mm [24.3, 28.3 mm]; P = .003) and descending aorta diameter (14.7 mm [12.2, 16.8 mm] vs 22.5 mm [19.8, 24.0 mm]; P < .001). ConclusionsCFD analysis reveals hemodynamic changes in the aorta of patients with TA. The applicability of CFD technique coupled with standard imaging assessments in predicting disease progression of such patients will be explored in future studies. Future large cohort study with outcome correlation is also warranted. Clinical RelevanceBased on patient-specific computational fluid dynamics simulations, the present retrospective study revealed significant difference in aortic hemodynamics between the patients with and without Takayasu arteritis (TA). To the best of our knowledge, this study is the first to evaluate hemodynamic conditions within TA, demonstrating the potential of computational flow modeling in capturing abnormal hemodynamic forces, such as high wall shear stress, resulted from irregular morphological changes. In the future, assessing the hemodynamic parameters within patients with TA during the prestenotic period, together with longitudinal computational fluid dynamics studies may allow better monitoring and management of TA.

Hemodynamic analysis of carotid endarterectomy

Atherosclerotic stenosis of the carotid artery may lead to cerebral infarction, stroke, and other serious consequences, and it is usually treated clinically with carotid endarterectomy. By comparing the pre- and postoperative flow fields, it can be shown that the operation improves hemodynamic parameters, such as the velocity, wall shear stress, and wall pressure of the local flow field of the carotid artery. However, previous studies have rarely considered the difference between postoperative and healthy carotid flow fields, and thus, the cause of any postoperative restenosis may remain hidden. Therefore, this study constructed preoperative, postoperative, and (hypothetically) healthy carotid artery models based on the real vascular structure data of a patient and applied numerical simulations verified by physical models to compare hemodynamic parameters, such as flow rate, flow state, and wall shear. The results showed that after the operation, the maximum carotid blood flow velocity decreased from 2.8 to 1.02 m/s, the maximum wall shear stress decreased from 190 to ∼75 Pa, the wall pressure of the carotid inlet recovered from 3000 to 400 Pa, and the vortex in the distal internal carotid artery disappeared. In addition, this study also found a vortex and the low-level wall shear stress of approximately 5 Pa remained in the carotid bifurcation after the operation, which also lacked spiral flow, unlike the healthy model. Therefore, due to the morphological differences between the postoperative and healthy carotid artery, adverse hemodynamic factors and a potential risk of postoperative restenosis will remain after the procedure.

Long-term prognostic impact of paravalvular leakage on coronary artery disease requires patient-specific quantification of hemodynamics.

Transcatheter aortic valve replacement(TAVR) is a frequently used minimally invasive intervention for patient with aortic stenosis across a broad risk spectrum. While coronary artery disease(CAD) is present in approximately half of TAVR candidates, correlation of post-TAVR complications such as paravalvular leakage(PVL) or misalignment with CAD are not fully understood. For this purpose, we developed a multiscale computational framework based on a patient-specific lumped-parameter algorithm and a 3-D strongly-coupled fluid-structure interactionmodel to quantify metrics of global circulatory function, metrics of global cardiac function and local cardiac fluid dynamics in 6 patients. Based on our findings, PVL limits the benefits of TAVR and restricts coronary perfusion due to the lack of sufficient coronary blood flow during diastole phase (e.g., maximum coronary flow rate reduced by 21.73%, 21.43% and 21.43% in the left anterior descending (LAD), left circumflex (LCX) and right coronary artery (RCA) respectively (N = 6)). Moreover, PVL may increase the LV load (e.g., LV load increased by 17.57% (N = 6)) and decrease the coronary wall shear stress (e.g., maximum wall shear stress reduced by 20.62%, 21.92%, 22.28% and 25.66% in the left main coronary artery (LMCA), left anterior descending (LAD), left circumflex (LCX) and right coronary artery (RCA) respectively (N = 6)), which could promote atherosclerosis development through loss of the physiological flow-oriented alignment of endothelial cells. This study demonstrated that a rigorously developed personalized image-based computational framework can provide vital insights into underlying mechanics of TAVR and CAD interactions and assist in treatment planning and patient risk stratification in patients.

Numerical assessment of hemodynamic perspectives of a left ventricular assist device and subsequent proposal for improvisation

Due to the unavailability of donors, the use of left ventricular assist devices has emerged to be a reliable line of alternative treatment for heart failure. However, ventricular assist devices (VAD) have been associated with several postoperative complications such as thrombosis, hemolysis, etc. Despite considerable improvements in technology, blood trauma due to high shear stress generation has been a major concern that is largely related to the geometrical feature of the VAD. This study aims to establish the design process of a centrifugal pump by considering several variations in the geometrical feature of a base design using the commercial solver ANSYS-CFX. To capture the uncertain behavior of blood as fluid, Newtonian, as well as non-Newtonian (Bird-Carreau model), models are used for flow field prediction. To assess the possibility of blood damage maximum wall shear stress and hemolysis index have been estimated for each operating point. The results of the simulations yield an optimized design of the pump based on parameters like pressure head generation, maximum shear stress, hydraulic efficiency, and hemolysis index. Further, the design methodology and the steps of development discussed in the paper can serve as a guideline for developing small centrifugal pumps handling blood.

Hemodynamics and bio-mechanics of morphologically distinct saccular intracranial aneurysms at bifurcations: Idealised vs Patient-specific geometries

Background and Objective.Understanding the factors that influence the rupture of aneurysms is of primary concern to the clinicians, who are grappled with patient management. It is important to know how the relation between morphological features of the cerebral aneurysm, and the mechanical stresses on the containing arterial walls are influenced by the hemodynamic forces. Present study investigates three different shapes, which have been identified correspondingly in patient-specific scenarios as well. The primary objective is to categorize the bifurcation aneurysms into standard shapes such as, spherical, beehive and pear-shaped, based on patient-specific clinical studies and further compare and contrast the model aneurysms with the patient specific configurations, for their hemodynamic factors as well as the attendant stresses on the wall.MethodsComputational fluid dynamic simulations are performed accounting for the fluid-structure interaction (FSI) effects between the flowing fluid and the containing vessel wall. Blood is assumed to be Newtonian, while the arterial walls are assumed to be linearly elastic. A commercial solver is used for performing detailed calculations. Hemodynamic and bio-mechanical rupture predictions are carried out for the three different shapes. Observations derived from the idealised simulations are compared and contrasted against their patient-specific counterparts.ResultsFrom detailed numerical simulations, it was observed that pear-shaped aneurysms exhibit large re-circulation bubble and flow stagnation zone, with higher residence time for the particles, which may lead to atherosclerotic lesions. Beehive shape allows for maximum flow into the aneurysmal sac with concentrated jet impinging on the dome, leading to high values of maximum WSS (MWSS) resulting in great propensity to form a secondary bleb. However, flow field inside a spherical aneurysm is found to be stable with fewer vortices, and nearly uniform distribution of wall stresses are observed though-out the sac, which perhaps signifies hemodynamically and bio-mechanically stable condition.ConclusionCategorizing patient-specific intracranial aneurysms into standard shapes viz, spherical, beehive and pear could generalize the process of prediction of hemodynamic and bio-mechanical rupture indicators. Comparative assessment of the flow field and stresses reported from the simulations on idealised models, with corresponding patient-specific simulations reveal that, these studies could aid in understanding the generalised shape dependence of hemodynamic and bio-mechanical behaviour of aneurysms.

P068 Computational fluid dynamic study in Obstructive Sleep Apnea patients

Abstract Introduction Obstructive sleep apnea (OSA) is a common disorder which may need surgery to widen the airway. However, the success rate of surgery is variable. Thus, it is necessary to predict the outcome of the surgery preoperatively. The purpose of this study is to evaluate the mechanical parameter of upper airway airflow in OSA patients using computational fluid dynamics (CFD) method. Method We conducted a study on the patients with snoring, underwent the full night polysomnograpny (PSG) and paranasal sinus computed tomography(CT). The patients with past history of previous trauma or surgery were excluded. Three-demensional reconstructions of the upper airway were created in the medical imaging software Mimics 16.0 using paranasal CT. The reconstructions extended from nasopharynx to hypopharynx. Steady-state, turbulent, inspiratory airflow simulations were conducted in Fluent 17.0 with following boundary conditions The mechanical parameters (wall shear stress, pressure, plane velocity) were calculated in the three levels of nasopharynx, retropalatal, retrolingual area. Results The maximum wall shear stress values were shown at the retropalatal plane in all patients. There is a tendency for the wall shear stress value of the retropalatal area to increase as the AHI increases. The maximum velocity values were shown at the retropalatal plane in all patients. The maximum pressure values were shown at the nasopharynx plane in all patients. Conclusion the maximum wall shear stress values were shown at the retropalatal plane and the wall shear stress value of the retropalatal area increased as the AHI increased. Thus, the palatal surgery might help the OSA patients.

Localized Elevation of Wall Shear Stress Is Linked to Recent Symptoms in Patients with Carotid Stenosis

Background: Estimation of symptomatic and asymptomatic carotid atherosclerosis differences can be the basis for prevention and management of carotid artery stenosis disease. In clinical practice, carotid plaque vulnerability is assessed only on the basis of luminal stenosis. However, the evolution of carotid plaque from an asymptomatic state to a symptomatic one is a complex process and the underlying hemodynamic mechanisms are unknown. We aimed to investigate the differences in hemodynamic parameters between patients with recently symptomatic carotid stenosis and asymptomatic ones. Methods: Hemodynamic simulations were performed on 26 carotid plaques from 25 patients with carotid artery stenosis ≥50%, 16 of whom had recent cerebrovascular ischemic events. Using human-specific flow parameters and 3D reconstruction of carotid computed tomography angiography images, we assessed hemodynamic characteristics such as wall shear stress (WSS), time-averaged WSS (TAWSS), oscillatory shear index, and relative residence time (RRT) during the cardiac cycle in patients with and without symptoms. Results: We found that symptomatic carotid stenosis patients had greater local TAWSS (99.59 ± 26.29 vs. 60.40 ± 20.46 dyn/cm², p = 0.0007) and maximal WSS (116.65 ± 39.11 vs. 68.28 ± 23.67 dyn/cm², p = 0.003), but lower RRT (0.019 ± 0.006 vs. 0.013 ± 0.069 s, p = 0.049), than asymptomatic patients, but this hemodynamic difference was not associated with carotid stenosis severity (p = 0.70). Patients with transient ischemic attack (TIA) or stroke had higher local TAWSS and WSSmax than patients with asymptomatic stenosis (p < 0.05). Subgroup analysis showed that there was no statistical difference in local hemodynamic variables between TIA and stroke patients with carotid artery stenosis. Conclusions: Patients with carotid artery stenosis are more likely to experience acute ischemic cerebrovascular accidents if they have higher WSS. Simultaneous assessment with hemodynamic parameters like WSS along with stenosis severity may aid risk stratification in patients with asymptomatic carotid artery stenosis.

In silico modeling for personalized stenting in aortic coarctation

Stent intervention is a recommended therapy to reduce the pressure gradient and restore blood flow for patients with coarctation of the aorta (CoA). A remaining challenge for physician is to select the optimal stent before treatment. Here, we propose a framework for personalized stent intervention in CoA using in silico modeling, combining image-based prediction of the aortic geometry after stent intervention with prediction of the hemodynamics using computational fluid dynamics (CFD). Firstly, the blood flow in the aorta, whose geometry was reconstructed from magnetic resonance imaging (MRI) data, was numerically modeled using the lattice Boltzmann method (LBM). Both large eddy simulation (LES) and direct numerical simulation (DNS) were considered to adequately resolve the turbulent hemodynamics, with boundary conditions extracted from phase-contrast flow MRI. By comparing the results from CFD and 4D-Flow MRI in 3D-printed flow phantoms, we concluded that the LBM-based LES is capable of obtaining accurate aortic flow with acceptable computational cost. In silico stent implantation for a patient with CoA was then performed by predicting the deformed geometry after stent intervention and predicting the blood flow. By evaluating the pressure drop and maximum wall shear stress, an optimal stent is selected.

Hemodynamic Effect of Pulsatile on Blood Flow Distribution with VA ECMO: A Numerical Study.

The pulsatile properties of arterial flow and pressure have been thought to be important. Nevertheless, a gap still exists in the hemodynamic effect of pulsatile flow in improving blood flow distribution of veno-arterial extracorporeal membrane oxygenation (VA ECMO) supported by the circulatory system. The finite-element models, consisting of the aorta, VA ECMO, and intra-aortic balloon pump (IABP) are proposed for fluid-structure interaction calculation of the mechanical response. Group A is cardiogenic shock with 1.5 L/min of cardiac output. Group B is cardiogenic shock with VA ECMO. Group C is added to IABP based on Group B. The sum of the blood flow of cardiac output and VA ECMO remains constant at 4.5 L/min in Group B and Group C. With the recovery of the left ventricular, the flow of VA ECMO declines, and the effective blood of IABP increases. IABP plays the function of balancing blood flow between left arteria femoralis and right arteria femoralis compared with VA ECMO only. The difference of the equivalent energy pressure (dEEP) is crossed at 2.0 L/min to 1.5 L/min of VA ECMO. PPI’ (the revised pulse pressure index) with IABP is twice as much as without IABP. The intersection with two opposing blood generates the region of the aortic arch for the VA ECMO (Group B). In contrast to the VA ECMO, the blood intersection appears from the descending aorta to the renal artery with VA ECMO and IABP. The maximum time-averaged wall shear stress (TAWSS) of the renal artery is a significant difference with or not IABP (VA ECMO: 2.02 vs. 1.98 vs. 2.37 vs. 2.61 vs. 2.86 Pa; VA ECMO and IABP: 8.02 vs. 6.99 vs. 6.62 vs. 6.30 vs. 5.83 Pa). In conclusion, with the recovery of the left ventricle, the flow of VA ECMO declines and the effective blood of IABP increases. The difference between the equivalent energy pressure (EEP) and the surplus hemodynamic energy (SHE) indicates the loss of pulsation from the left ventricular to VA ECMO. 2.0 L/min to 1.5 L/min of VA ECMO showing a similar hemodynamic energy loss with the weak influence of IABP.

A prediction model of wall shear stress for ultra-high-pressure water-jet nozzle based on hybrid BP neural network

ABSTRACT Two hybrid back-propagation neural network (BPNN) models optimized by two heuristic search algorithms, namely genetic algorithm (GA-BP) and particle swarm optimization (PSO-BP), are proposed in this paper to predict radial maximum wall shear stress instead of traditional computational fluid dynamics (CFD) methods. The two proposed models are trained and validated using a database of 150 radial maximum wall-shear-stress values obtained via CFD simulations. The best fit model is identified from various BPNN models based on the Akaike information criterion (AIC) and the Bayesian information criterion (BIC), balancing the trade-off between goodness-of-fit and model complexity. The model performance is evaluated by MAE, RMSE, regression coefficient (R), and Nash-Sutcliffe efficiency (NSE). The best fit model is a three-layered BPNN model consisting of a 4:4:1 topology. In almost all evaluation indicators, the two hybrid BPNN methods outperform three existing algorithms, namely classical BPNN, random forest (RF), and gradient boosting decision tree (GBDT). Both PSO-BP and GA-BP can provide a more precise assessment of radial maximum wall shear stress, with maximum errors being 5.81% and 8.24% respectively. The proposed PSO-BP prediction model is promising and has great feasibility in predicting the radial maximum wall shear stress of UHP water-jet nozzle in engineering applications.

EFFECTS OF SAND THERAPY ON FLUID DYNAMICS OF BLOOD IN THE POPLITEAL ARTERY BASED ON THE EULER MULTIPHASE MODEL

The effect of sand therapy on the hemodynamics of the popliteal artery (POA) was investigated to elucidate its mechanism in atherosclerosis physiotherapy. The hemodynamic parameters of the POA before and after sand therapy were obtained from 58 subjects and statistically analyzed. A three-dimensional finite element model of POA bifurcation was established. Blood was regarded as a triple-phase flow composed of plasma, red blood cells (RBCs), and white blood cells (WBCs). Using computational fluid dynamics (CFD), blood flow velocity, wall shear stress (WSS), and blood cell volume distribution before and after sand therapy were calculated. Sand therapy could reduce the vortex and reflux in blood vessels. The maximum increase in blood axial velocity was 34.38%. The maximum WSS increased by 22.82 Pa and the blood cells gradually moved away from the vessel wall and toward the axis of the blood vessel. The reduction in vortex and reflux, and the increase in blood axial velocity after sand therapy are beneficial in reducing the accumulation of cholesterol and other substances, thereby alleviating the formation of atherosclerotic plaques and lipid streaks. The rise in WSS slows the tendency of arterial vascular thickening in regions of low WSS. The movement of blood cells to the axis of blood vessels can reduce the possibility of thrombosis caused by blood cells squeezing on the blood vessel walls. These findings suggest that sand therapy may slow atherosclerosis progression.

Aortic Dissection is Determined by Specific Shape and Hemodynamic Interactions.

The aim of this study was to determine whether specific three-dimensional aortic shape features, extracted via statistical shape analysis (SSA), correlate with the development of thoracic ascending aortic dissection (TAAD) risk and associated aortic hemodynamics. Thirty-one patients followed prospectively with ascending thoracic aortic aneurysm (ATAA), who either did (12 patients) or did not (19 patients) develop TAAD, were included in the study, with aortic arch geometries extracted from computed tomographic angiography (CTA) imaging. Arch geometries were analyzed with SSA, and unsupervised and supervised (linked to dissection outcome) shape features were extracted with principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA), respectively. We determined PLS-DA to be effective at separating dissection and no-dissection patients ([Formula: see text]), with decreased tortuosity and more equal ascending and descending aortic diameters associated with higher dissection risk. In contrast, neither PCA nor traditional morphometric parameters (maximum diameter, tortuosity, or arch volume) were effective at separating dissection and no-dissection patients. The arch shapes associated with higher dissection probability were supported with hemodynamic insight. Computational fluid dynamics (CFD) simulations revealed a correlation between the PLS-DA shape features and wall shear stress (WSS), with higher maximum WSS in the ascending aorta associated with increased risk of dissection occurrence. Our work highlights the potential importance of incorporating higher dimensional geometric assessment of aortic arch anatomy in TAAD risk assessment, and in considering the interdependent influences of arch shape and hemodynamics as mechanistic contributors to TAAD occurrence.